Most of the energy used in the world is derived from the combustion of carbon and hydrogen-containing fuels such as coal, oil and natural gas. In addition to carbon and hydrogen, these fuels contain oxygen, moisture and contaminants. Flue gas is a byproduct of the combustion of the fuels and can contain ash, sulfur (often in the form of sulfur oxides, referred to as “SOx”), nitrogen compounds (often in the form of nitrogen oxides, referred to as “NOx”), chlorine, mercury, and other trace elements. Awareness regarding the damaging effects of the contaminants released during combustion triggers the enforcement of ever more stringent limits on emissions from power plants, refineries and other industrial processes. There is an increased pressure on operators of such plants to achieve near zero emission of contaminants.
Numerous processes and systems have been developed in response to the desire to achieve near zero emission of contaminants Systems and processes include, but are not limited to selective catalytic reduction (SCR) systems, desulfurization systems (known as wet flue gas desulfurization “WFGD” and dry flue gas desulfurization “DFGD”), particulate filters (including, for example, bag houses, particulate collectors, and the like), as well as the use of one or more sorbents that absorb contaminants from the flue gas.
Chemical reactions on a solid catalyst surface of commercial SCR systems convert NOx to N2. Typically the solid catalysts are disposed on a substrate formed in a grid configured to allow the flue gas to flow through the grid and react with the catalyst. One problem with SCR system is that activity of the catalyst depends on temperature and flue gas constituents and deteriorates over time. For example, catalysts may require replacement prematurely due to erosion caused by localized high velocities of the flue gas through portions of the grid. However, controlling the velocity of the flue gas entering the grid can be difficult because typically flue gas enters the SCR generally horizontally from a side and must turn and change to a downward direction at an inlet of the grid. Apparatuses for changing the direction of the flue gas and attempting to establish a uniform velocity profile of the flue gas entering the grid are typically large and add significant height to a SCR. Such apparatuses are heavy, difficult to install and the increased SCR height results in increased cost. Accordingly, there is a need for a more compact and effective flow control grid that can change the direction of fluid flow and create a substantially uniform velocity profile at the outlet thereof.